In global navigation satellite systems (GNSS), data received from satellites is used to triangulate a position of a GNSS receiver. The GNSS receiver uses ephemeris and timing data to calculate a position of a number of satellites at a given time and determines its own position relative to the satellites.
In these systems, a GNSS receiver may receive a line of sight LoS signal directly from the satellite as well as multi-path MP signals. The multi-path signals are signals originating at a satellite and received at the receiver via reflection by the surrounding environment.
These multi-path signals may form constructive and destructive interference with corresponding LoS signals. The resultant signal processed by the GNSS receiver may be distorted by the multi-path components and may affect an accuracy of a position calculated by the GNSS receiver.
According to a first aspect there is provided a method for detecting multi-path interference in a spread-spectrum signal comprising: comparing a variation of a first signal corresponding to a correlation of the spread-spectrum signal and a spreading code having a first offset and a variation of a second signal corresponding to a correlation of the spread-spectrum signal and the spreading code having a second offset; and detecting multi-path interference in dependence on the comparison.
The first and second signals may be offset with respect to a phase of the spread-spectrum signal. The phase of the spread-spectrum signal may be acquired by a receiver.
The first signal may be a measurement of the correlation between the spread-spectrum signal and the spreading code having the first offset and the second signal may be a measurement of the correlation between the spread-spectrum signal and the spreading code having the second offset.
The first and second offsets may be respective negative and positive offsets with respect to the phase of the spread-spectrum signal. The first and second signals may be generated by a tracking loop of a spread-spectrum receiver.
The step of comparing may comprise determining a relationship between the first and second signal. The relationship may be a relationship of a power variation of the first and the second signal. The step of detecting multi-path interference may comprise determining whether the determined relationship falls within a range.
The range may correspond to an allowed power variation of the second signal. The power variation of the second signal may correspond to a level of multi-path interference in the spread-spectrum signal. The relationship may correspond to a ratio of the power variation of the first signal to the power variation of the second signal.
The method may further comprise: receiving a spread-spectrum signal; acquiring the phase of the spread-spectrum signal; and tracking the spread-spectrum signal. Tracking the spread-spectrum signal may further comprise adjusting the phase of the spread-spectrum signal.
According to a second aspect, there is provided an apparatus for detecting multi-path interference in a spread-spectrum signal comprising a processing unit configured to compare a variation of a first signal corresponding to a correlation of the spread-spectrum signal and a spreading code having a first offset and a variation of a second signal corresponding to a correlation of the spread-spectrum signal and the spreading code having a second offset, and detect multi-path interference in dependence on the comparison.
The first and second signals may be offset with respect to a phase of the spread-spectrum signal. The processing unit may be further configured to acquire the phase of the spread-spectrum signal.
The first signal may be a measurement of the correlation between the spread-spectrum signal and the spreading code having the first offset and the second signal may be a measurement of the correlation between the spread-spectrum signal and the spreading code having the second offset.
The first and second offsets may be respective a negative and positive offsets with respect to the phase of the spread-spectrum signal. The first and second signals may be generated by a tracking loop of a spread-spectrum receiver.
The processing unit may be further configured to determine a relationship between the first and second signal. The relationship may be a relationship of a power variation of the first and second signal.
The processing unit may be further configured to determine whether the determined relationship is within a range. The range may correspond to an allowed power variation of the second signal. The power variation of the second signal may correspond to a level of multi-path interference in the spread-spectrum signal. The relationship may correspond to a ratio of the power variation in the first signal to the power variation in the second signal.
According to a third aspect, there is provided a spread-spectrum receiver comprising: receiver circuitry configured to receive a spread-spectrum signal; the receiver being configured to receive a plurality of channels and having a processing unit configured to for each channel, acquire a phase of the spread-spectrum signal and track the spread-spectrum signal; the processing unit being further configured to compare a variation of a first signal corresponding to a correlation of the spread-spectrum signal and a spreading code having a first offset and a variation of a second signal corresponding to a correlation of the spread-spectrum signal and the spreading code having a second offset, and a detect multi-path interference in dependence on the comparison.
According to a fourth aspect, there is provided a mobile terminal comprising the spread-spectrum receiver according to the third aspect.
According to a fifth aspect, there is provided a satellite navigation positioning unit comprising the spread-spectrum receiver according to the third aspect.